The present invention relates generally to a friction plate and assembly for use in clutches or brake assemblies for transmissions, differentials or brake systems. Specifically, the present invention relates to a waved friction plate having selectively applied friction material that exposes crests and troughs of a waved plate core. The exposed crests and troughs of the friction plate act as low rate springs to push the waved friction plate away from a separator plate to reduce power loss from shearing of cooling fluid.
Plate and facing assemblies are known in the art and are used in multi-disk friction devices such as clutches or brakes. The friction devices are used in different capacities, and are commonly found in vehicle power train and brake applications. The power train""s main component is typically referred to as xe2x80x9ca transmissionxe2x80x9d. Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. Transmissions include one or more gear sets which may include an inner sun gear, intermediate planet gears which are supported by their carriers, and outer ring gears. Various components of the gear sets are held or powered to change the gear ratios in the transmission. The multi-disk pack clutch is a friction device which is commonly employed in a transmission or differential. In addition, multi-disk friction devices are also used in industrial applications such as wet brakes, for example, to brake the wheels on earth moving equipment.
A multi-disk pack clutch or brake assembly includes a clutch subassembly having a set of flat plates and a set of flat friction disks which are interleaved between one another. The friction plate is a flat annular plate mounted on a cylindrical core which cooperates with a flat annular separator plate. Various types of friction materials are secured on the core plate and are arranged in different configurations in order to provide flow passages for the cooling fluid. The plates and friction disks are immersed in a continual flow of lubricant material. In an open pack operation the friction disks and separator plate normally turn past one another with nominal contact. The clutch or plate assembly also includes a piston. In certain applications, it is known to employ several multi-disk pack friction devices in combination in order to establish different drive connections throughout the transmission or differential in order to provide various gear ratios in operation.
The confronting faces of the interleaved plates and disks are covered with frictional materials. When a friction device is engaged, kinetic energy is converted into thermal energy and a considerable amount of heat is generated. If the frictional surfaces of the disks and plates gets too hot, the plates or disks can suffer thermal damage. This causes damage to the friction material and degrades the clutch or brake operational effectiveness. Therefore, it is desired to have the heat which is generated when the friction device is engaged be efficiently dissipated.
For friction materials that are used in passenger car transmissions, for example, it is desired that the friction materials have a high dynamic coefficient of friction and a low static coefficient of friction so that there is little shudder or shock during engagement of the clutch or brake assembly. Typically, the coefficient of friction for friction material-on-steel is about 0.12.
Accordingly, there is a need for a friction plate that is both durable and shudder resistant.
It is a primary object of the present invention to reduce open pack spin losses.
Other objects and advantages of the present invention will become apparent to those skilled in the art upon a review of the following detailed description of the preferred embodiments and the accompanying drawings.
A friction plate has a waved or sinusoidal annular shape. The waved friction plate defines at least one crest and trough. Friction material is selectively applied to at least one side of the waved friction plate such that at least one area or section of the waved plate has no friction material thereon. The exposed section of the waved friction plate allows metal-to-metal contact between the waved friction plate and an adjacent separator plate during opening pack operating conditions.
The crests and troughs of the waved friction plate cause the waved plate to act as a low rate spring. The waved friction plate is pushed away from the separator plates thereby reducing power losses due to shearing of the automatic transmission fluid.